Sewage slope calculation: formulas and regulations

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The sewage system is a network of pipelines, functional units, modules and standard components. The whole set is designed to ensure the smooth passage of wastewater. It is obvious that the spontaneous movement of household waste in the pipes is possible if the pitch was observed during their installation.

From the article proposed by us you will learn how to calculate the slope of the sewer. After all, this is not an arbitrary value: the slope should provide for the movement of stocks with the speed necessary for the normal operation of the system. We will describe how the parameter important for sewage is determined.

The content of the article:

  • The device sewer network: rules and regulations
  • About the calculation of sewer networks
  • Other rules (rules) of installation
    • Closed communications equipment
    • Which pipes are suitable for the system?
    • Features of installation of risers
    • Open and closed lines
  • Bookmark sewer pipes
  • Conclusions and useful video on the topic

The device sewer network: rules and regulations

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Installation of household and any other sewage system is clearly explained by the SNiP. Moreover, the explanations in the documents are the rules and regulations that professional builders strictly follow.

Domestic construction with their own hands, of course, difficult to equate to professional activity. But this moment does not remove from the house master assembly obligations. Therefore, each builder is recommended to know how the calculation of sewage.

Calculation of sewage for a private house

The construction of sewer communications in residential buildings is associated with the need for calculation. The main goal of sewage calculations is to comply with the permissible norms of pipeline slope and compliance with the environmental conditions of operation. Ignoring calculations turns into serious problems.

It would seem, why go into all the subtleties of calculations? Does anything drastically change in the sewage system, if you make the slope of the pipes a little less or a little more than the existing parameters of the SNiP?

So, the practice of operating communications shows that even small deviations of the slope values ​​from the established norms can disrupt the normal operation of the sewage system.

For example, the owner of a private house makes the sewage with his own hands and does not own the method of calculation. He takes and lays the slope of pipelines "by eye". As a result, gets the value of the slope of household sewage less than standard figures.

The slope of household and industrial sewage pipes

If the sewage system in the house or at industrial facilities does not comply with the pipe slope norms, the principle of self-cleaning of sewer networks is violated. This leads to the periodic formation of congestion, you often have to perform unplanned cleaning communications

The speed of movement of the fecal environment is reduced, at first insignificant congestion, followed by massive, difficult to penetrate. Finally, the line is completely hammered, the task of global cleansing is on the agenda. And such a system operation, with insufficient pitch of the pipes, promises an enviable constancy of congestion and unpleasant odors.

Another point: a non-professional master mounts the sewers on a slope that exceeds the statutory figures. The increased slope of the sewage pipelines contributes to an increase in the velocity of the liquid medium, but at the same time a so-called “separation effect” is formed.

Liquid, which is higher than the self-cleaning speed, is separated from the solid mass, which remains on the pipe walls. Over time, the residual masses build up, and the result is the same - congestion, odors, cleaning.

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Slope of sewer lines

The slope of the horizontally oriented sewer lines is necessary for the implementation of spontaneous flow towards the receiving equipment and unloading

Device external sewer branches

Pipes with a slope are stacked during the construction of internal branches of the sewer system and external lines leading to sewage treatment, accumulation or discharge points.

Construction of lines with pipes of different diameters

For home craftsmen who do not want to spend time on calculations, the allowable slopes are provided for in building codes, normal and lowest values ​​are given

Example of laying sewers with a slope

Sewer lines, assembled from pipes Ø 110 mm, are arranged with a normal and least slope, which should be 0.02 / 0.012. For pipes Ø 50 mm the same values ​​are 0.035 / 0.025

The slope of sewer pipes of large diameter

The standard and the smallest slope of pipes Ø 150 mm in the building directories is 0.01 / 0.007. Same values ​​for pipes Ø 200 mm 0.008 / 0.005

The slope of the external sewer pipeline

The slope of the external sewer branches must be at least 0.02, that is, not less than 2 cm per linear meter of the system

Laying of drainage and storm sewer pipes

Laying drains - perforated pipes that absorb groundwater in flooded areas, put with a smaller incline, from 0.001 to 0.003, so that the system has time to collect enough water to drain

Slope of sewer branch

The slope of the drainage line should be 135º. If necessary, immediately after the system is taken out of the house, a water seal is arranged from pipes of the same diameter as the pipeline.

Slope of sewer lines

Slope of sewer lines

Device external sewer branches

Device external sewer branches

Construction of lines with pipes of different diameters

Construction of lines with pipes of different diameters

Example of laying sewers with a slope

Example of laying sewers with a slope

The slope of sewer pipes of large diameter

The slope of sewer pipes of large diameter

The slope of the external sewer pipeline

The slope of the external sewer pipeline

Laying of drainage and storm sewer pipes

Laying of drainage and storm sewer pipes

Slope of sewer branch

Slope of sewer branch

Properly set slope values ​​are a guarantee of a long and reliable system operation.

About the calculation of sewer networks

The speed of movement of the economic-fecal environment, at which the self-cleaning effect is achieved, is mathematically calculated by the formula:

The formula for calculating the slope of sewage

This mathematical formula is used to calculate household and industrial sewage. In particular, using the formula calculates the desired slope of sewer pipes


  • V - the velocity of the liquid medium (not less than 0.7 m / s);
  • H / d - filling the sewer pipe (at least 1/3 of the volume);
  • K - coefficient of resistance, depending on the material of the pipeline (0.5 - plastic, glass; 0.6 - other).

Practical appliance of household and industrial sewage system allows situations when conditions calculated by the specified formula is not possible to perform due to low consumption sewer drains.

In this case, it is recommended to install communications from pipes with a diameter of up to 50 mm with a slope of 3 mm per 1 meter of length. Pipelines with a diameter of 85-100 mm shall be laid with the observance of a standard slope of 2 mm per 1 meter of length. In any case, the maximum allowable value of the slope rate may be 15 mm per meter of length, but no more.

If the system of sewer networks uses a cradle mechanism for transporting wastewater, in this case there is also a standard. Thus, the filling level of trays should not exceed 0.8 of the size of their height. The width of the sewer tray can not be less than 200 mm.

And the width of the tray is set based on the calculation of the hydraulic properties of the system and the design features of this element. So, sewer trays in height more than 500 mm in the size of width should not be less than 700 mm.

The rate of calculation of the slope of the trays

Tray sewage system in the same way as the pipe, is mounted in compliance with the established norms of slope. In addition, tray systems are constructed taking into account the size of the individual elements of the line - depending on the size of the height and width

Trays in the construction of sewage systems are used in the installation of storm and drainage systems. With the calculation slope drainage pipes read the article, which we highly recommend to read.

Wastewater filled with a high content of mechanical suspensions is discharged along sewage lines made with a slope, the value of which is also determined by calculation taking into account the provision of self-cleaning speeds in pipes fluid.

Filling of pipelines is normalized by the value of 1/3 of their volume. Typically, this type of effluent refers to industrial products, where mechanical particles are particles of metals and other solids.

Other rules (rules) of installation

The provisions of the regulatory documentation affect both the characteristics of the equipment involved in the sewer system, and the nuances of the installation itself.

Closed communications equipment

For most cases, the design of household sewer communications norms (rules) provide for the execution of closed lines of pipelines. Such a scheme traditionally works on the principle of movement of economic and fecal waters by gravity.

At some sites (mostly industrial), where wastewater is discharged without the presence of odors and hazardous fumes, it is permissible to carry out communications on the basis of gravity chutes. At the same time, it is required to equip gutter lines with a hydraulic lock device.

Straight line sewer

Laying sewage pipelines is always straightforward. To create turns, bends, forks, additional mounting elements are used. From the starting point of the line installation to its full completion, it is necessary to withstand a uniform change in the slope according to the calculations

If we consider the system in the plan, then each individual section sewer communications it is mounted strictly rectilinearly. If you want to change the direction of laying pipelines, apply the standard mounting components (angles, crosses, tees, transitions, etc.).

It is unacceptable to change the calculated slope of the sewer pipelines in a separate section of the completed line, mounted in a horizontal position.

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Formation of a slope of the external sewerage

To form a standard slope, trays are laid on the bottom of the trench or sand is poured, which is pounded and poured in, so that an inclined surface is obtained.

Gasket from the exit from the house to the point of unloading / cleaning

External sewage lines are laid from the exit of the house or bath and continue in the direction of the septic tank or drive. Into the sewage treatment plant or storage piping is in fact introduced at the device site.

Device openly laid branches

The slope of openly laid sewer pipes is arranged by fixing the canal on the wall with clamps. The pipes are first laid on bricks and scraps of boards, check the slope, then fix

Hidden pipeline

When laying the pipeline in a covert way, the slope forms a strobe, which is marked and laid with the required slope

Formation of a slope of the external sewerage

Formation of a slope of the external sewerage

Gasket from the exit from the house to the point of unloading / cleaning

Gasket from the exit from the house to the point of unloading / cleaning

Device openly laid branches

Device openly laid branches

Hidden pipeline

Hidden pipeline

Which pipes are suitable for the system?

In relation to sewage networks (household, industrial), as well as with emphasis on the properties of corrosion resistance and strength, various pipe modifications are used for sewage installation.

For communications made on the principle of free flow, the pipe materials are:

  • polymer compounds;
  • cast iron;
  • concrete;
  • glass;
  • asbestos cement.

Criteria and selection rules pipes for outdoor sewage are shown here. The information recommended by us will be useful to all zealous owners of country plots planned for construction.

Under the communications transporting liquids with a pressure, pipes are made of materials:

  • polymers;
  • cast iron;
  • asbestos cement;
  • reinforced concrete.

Internal sewage lines are mounted in one of two ways: open / hidden. Regardless of the method of installation, polymer pipes are widely used in installation. With landmarks of choice best pipes for sewage will introduce our recommended article.

Plastic sewage pipelines are allowed to be laid in the ground below the floor of buildings. But you should take into account the load attributable to the site with such communications.

Plastic pipes for sewer networks

The most common details of sewer communications. Plastic pipes and all necessary fittings are used when constructing networks for various purposes. For private property owners, this is an economical way to arrange sewage in the house.

Plastic fittings are considered as universal, can be successfully used for internal and external networks.

Features of installation of risers

Installation of risers inside residential buildings is done in canals, mines, boxes. Their design must comply with fire safety regulations. Mines, boxes, canals, etc., are necessarily equipped with removable panels.

Through the removal of panels provides access to communications. The use of removable panels made of materials capable of burning is allowed if the sewer line consists of PVC pipes. Panels of mines where polyethylene pipes are laid are usually made of fireproof materials.

Open and closed lines

Installation of open sewer pipes made of plastic is allowed to be performed inside the attic areas of residential buildings, as well as in basement areas.

The places of transition of sewer risers from the residential area to the attic area must be sealed with a cement solution, with a minimum thickness of 20-30 mm. The same mixture protects the area of ​​the pipe above the level of overlap by 80-100 mm; moreover, before sealing with cement, a waterproofing material is applied to the surface of the pipeline.

Laying of internal sewer lines is prohibited in the structure of the floors, inside the walls, in the area of ​​the ceiling of the rooms of the housing stock. A number of buildings and premises for other purposes, where a special sanitary regime is provided for, fall under the same requirements.

If it is necessary to lay a drain pipe from the sink of the bath or kitchen sink, this is done above the floor level using waterproofing equipment, followed by lining the installation zone.

Ventilation riser over the roof of the house

Part of the home sewage system is the ventilation riser. It is an integral part of professionally executed household sewage. The norms and rules of installation also apply to the ventilation risers of household sewage. For example, the minimum allowable diameter dimensions of the pipes used are specified.

It is not allowed to combine sewage for domestic and industrial use if industrial effluents contain liquids of a toxic nature or are highly flammable. Sewerage networks of any type, the scheme of which provides for the disposal of wastewater to the external sewage system, should be equipped with ventilation risers.

Upper limit switches ventilation pipes It is necessary to lead through the thickness of the roof and raise it to a height:

  1. For flat roofing (at least 300 mm).
  2. For pitched roofing (at least 500 mm).

The indent in the horizontal direction from the outlet of the riser to the nearby windows and balconies of the building must be at least 4 meters.

Bookmark sewer pipes

Gasket sewer pipeline with a slope - This is only part of the requirements for the general tab of the sewer network. You should also take into account the norms established under the laying of pipes, based on the risks of damage and destruction.

These norms are due to the effect of temporary and permanent loads on communications. For example, for living conditions, the laying of sewage pipes inside buildings is performed to a depth of at least 100 mm, if you take the floor surface and the upper outer wall of the sewer pipe as measurement points.

Pipelines domestic domestic sewage, mounted in places of possible mechanical impacts, it is recommended to protect them by restricting direct access to them. For these purposes, use of protective nets, trays, channels, etc.

If the pipeline is located below the seasonal freezing of soil layers, the technology should be applied sewer pipe insulation. The role of modern insulation is quite pretend rigid polyurethane foam. Also heat the sewer pipes with mineral wool with pre-waterproofing.

Warming of sewer pipelines

One of the possible options for thermal insulation of the sewer line. Different materials can be used for heat insulation of household sewage pipelines, but always give priority to heat insulators with low flammability properties or none at all.

When a trench is used as a place to lay communications, after developing such a design slope, it is recommended to perform soil compaction before laying pipes. Works on soil compaction are carried out on the area of ​​the bottom part of the trench along its entire length.

Seal the soil is required at least 200-300 mm depth. After these measures are completed, gravel is poured with a calculated slope in the trench or trays are laid and sewer pipes are placed in the trays.

Conclusions and useful video on the topic

Interesting and informative reflections on the correct slope of the sewer:

The organization of household waste water is not such a simple matter as an inexperienced man in the street can imagine. Professionals in the field of housing communications know that it is necessary to count laying of sewer networks in in each case of their construction, regardless of whether installation is carried out for a private house or an industrial system is made destination.

Please write comments, ask questions, post a photo in the block below. Tell us about how the sewer lines were laid on your own country plot, and whether you followed the specified slope. It is possible that your advice will be useful to site visitors.

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